This application is based on the Swedish patent application SE 9702659-5 xe2x80x98Compact Antenna Devicexe2x80x99 which is hereby incorporated by reference and the international patent application PCT/SE98/00899 xe2x80x98Compact Antenna Devicexe2x80x99 which is hereby incorporated by reference. Both applications have the same applicant as the present invention.
1. Technical Field of Invention
The present invention relates in general to an antenna structure and more specifically to a microstrip antenna structure.
2. Description of Related Art
With the recent advances in mobile communication, there has been tremendous interest in development of small size and low profile antennas for the further miniaturization of mobile radio communication equipment. Goals include small size, low profile, low cost and ease of manufacturing. Frequencies of interest can for instance be 900 MHz band antennas for applications in cellular handheld radio devices such as GSM (890-935 MHz), indoor cordless telephones such as the European CT1+ (886-931 MHz) and 1.9 GHz band antennas for applications in DECT (1.89 GHz) and PCS (1.8 GHz). These systems have their own requirements in antenna characteristics, such as resonant frequency, bandwidth, gain etc.
Existing antennas used in mobile phones include the most common whip antennas (monopole), microstrip patch antennas and planar inverted-F antennas. Microstrip patch antennas and planar inverted-F antennas are typically low-profile antennas. Although the microstrip patch antenna previously has had the shortcoming of narrow bandwidth and low efficiency, its advantages of low profile, small size and light weight are attractive properties.
However both planar inverted-F antennas and microstrip patch antennas exhibit size problems when they should be adjusted for the specific frequencies and fit into the newer generation of miniature mobile radio communication devices. This is particular problematic when modern mobile phone design calls for multiple antennas to be placed into one handset to be able to simultaneously communicate in two different systems, in a very broad frequency band or more generally to take advantage of antenna diversity.
EP 749 176xe2x80x98Planar and non-planar double C-patch antennas having different aperture shapesxe2x80x99 discloses a patch antenna. The C-patch antenna includes a truncated ground plane, a layer of dielectric material having a first surface overlaying the ground plane and an opposing second surface, and an electrically conductive layer. The conductive layer forms a radiating patch and has a non-rectangular aperture.
Wo 96/27219xe2x80x98Meandering inverted-F antennaxe2x80x99 discloses an inverted F-antenna with a meandering pattern. The antenna is a planar radiating structure having alternating cutouts along a longitudinal dimension of a planar radiating element or patch which is parallel to a nearly coextensive ground plane.
The object of the present invention is thus to achieve a small microstrip antenna device, mountable inside a hand-held radio communication device, for receiving and transmitting RF signals in one or more frequency bands.
The problems described above, with how to achieve an antenna which is mountable inside and hand-held radio communication device is solved by providing a microstrip antenna comprising a ground plane, at least a first feeding means and N radiating elements where N is an integer greater than zero. The micro strip antenna structure having a first conductive patch. The feeding means being arranged on the first patch for feeding radio frequency signals to the N radiating elements, at least a first of the N radiating elements having a second substantially rectangular patch. The second patch being inductively coupled to the first patch and the second patch having a free end.
In more detail the objects of the present invention according to one embodiment, is achieved by providing the above mentioned microstrip antenna structure wherein at least one of the N radiating elements having a capacitive coupling to ground in the free end.
In more detail the objects of the present invention according to one embodiment, is achieved by providing the above mentioned microstrip antenna wherein, the first and second patch being thin conductive layers on a dielectric substrate. The substrate comprising at least first and second protrusions arranged for retaining a component in electric contact with the first and second patch.
An advantage with the present invention is that a small microstrip antenna structure is achieved which is suitable for mounting inside a hand-held radio communication device.
Another advantage with the present invention is that the antenna structure can be tuned to be responsive to multiple frequencies.
An advantage, according to one embodiment of the invention, is that the antenna structure can be achieved with a choice of using discrete components or not.
An advantage, according to one embodiment of the invention, is that the antenna structure may be implemented directly on the inside of a back cover of a hand-held radio communication device.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only,- since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.